The wireless telecommunication terminal mentioned in the present invention is a terminal that can be carried by a user portably and capable of wireless communication, such as Personal Communication Service (PCS), Personal Digital Assistant (PDA), Smart Phone, International Mobile Telecommunication-2000 (IMT-2000) and a wireless Local Area Network (LAN) terminal. The embodiments of the present invention will be described hereinafter by taking an example of a folder-type wireless telecommunication terminal. A value λ0 is the wave length of an electromagnetic wave signal of a resonance frequency band radiated from each radiator.
Recently, wireless telecommunication terminals become miniaturized, as an integration technology of high frequency devices and a wireless telecommunication technology develop.
In particular, the size of an antenna for transmitting and receiving radio signals has been miniaturized according to the miniaturization trend of the wireless telecommunication terminal.
The antenna transforms an electric signal expressed as voltage/current into the electromagnetic wave signal and vice versa. That is, the antenna detects the electromagnetic wave signal radiated in the outside, i.e. free space, through an electromagnetism formed on a conductive wire, transforms the signal into the electric signal, resonates the electric signal from an end of the conductive wire into a particular frequency band, transforms the electric signal into an electromagnetic wave signal and radiates it to the outside.
The antenna is used for both transmission and reception of the wireless signal. That is, the antenna is so manufactured so as to fit characteristics of a particular frequency band in a planning or a manufacturing process. If the antenna is mounted in a transmit device for transmitting radio signals, it becomes a transmitting antenna. If it is set up in a wireless signal receiving device, it becomes a receiving antenna. If it is set up in a wireless signal transmitting/receiving device, it becomes a transceiving antenna.
Thus, if the antenna can transform an electric signal into an electromagnetic wave signal and radiate the signal to the outside, it is apparent that the antenna can transform the electromagnetic wave signal into the electric signal. Therefore, the embodiment of the present invention will be described only on the operation that an antenna transforms an electric signal into an electromagnetic wave signal and radiates the signal to the outside.
Meanwhile, a recent tendency is to mount a small antenna, so-called an intenna, in the inside of a wireless telecommunication terminal in order to make the exterior of the terminal beautiful.
FIG. 1 is a perspective view showing a conventional wireless telecommunication terminal with a built-in antenna.
As shown in FIG. 1, an embedded antenna 11 is mounted in upper one side of the inside of a body 10 in the wireless telecommunication terminal with the embedded antenna.
Although not shown in the drawing, the embedded antenna 11 is formed in such a manner that a plurality of radiators or conductive wires are connected to one feed point receiving an electric signal generated in the inside to process multi-frequency band signals.
FIG. 2 is a graph showing Voltage Standing Wave Ratio (VSWR) of the embedded antenna in a conventional wireless telecommunication terminal.
As shown in FIG. 2, in the frequency band 800 MHz of a Code Division Multiple Access (CDMA) method, VSWR values 20 and 21 are about 2.1:1 to 4.2:1, and the loss is serious in transmitting a signal due to the deterioration of impedance matching. This signifies that the antenna has poor performance.
Also, in the frequency band 1,800 to 1,900 MHz of a U.S. personal communication service (USPCS) method, the VSWR values 22 and 23 are about 2.4:1 to 3.0:1. This also shows that the antenna has poor performance.
A referential numeral 24 is a VSWR value in the frequency band 1,575 MHz of a Global Positioning System (GPS) method, which is 1.6:1.
Herein, the lower the Standing Wave Ratio of the antenna becomes, that is, the deeper a valley is formed in the graph becomes, the better an electric signal of the corresponding frequency band can flow on the conductive wire, thereby increasing the radiation efficiency of the electromagnetic wave signal.
However, since the antenna is embedded into the inside of the wireless telecommunication terminal in the conventional technology, the reflection and the refraction of the electromagnetic wave are caused by a metallic medium around a case and an antenna, which makes it difficult to radiate the electromagnetic wave signal intensely. Also, the narrow inner space of the wireless telecommunication terminal makes it difficult to radiate the electromagnetic wave signal having the multi-frequency band characteristics efficiently.
In particular, the conventional method has a problem that it is very difficult to radiate the electromagnetic wave signal of the multi-frequency band efficiently since the electromagnetic wave signal of a resonance frequency band having multi-frequency band characteristics has weak energy.
Also, the antenna is generally used in the VSWR range of 1.5. However, the problem of the conventional antenna is that the frequency bandwidth that can be embodied in the VSWR range of about 1.5 is too narrow.